About the supersonic/subsonic transition...

Gosh that was a beautiful conversation to read through. As a small aside, the spinning effect can actually work in real case scenarios and experimental airplanes have been flown that way, though not terribly effectively.

On the subject of all of the various bullet designs considered for transsonic regime, was there ever any experimentation done with forcing turbulent boundary layer flow, a la dimples/shot peened cases in the back half/last 1/3 of the bullet? Or any more airfoil-shaped bullets to perhaps not do so well in supersonic, but yet maintain momentum through the transsonic regime?
 
I tried modeling some dimpled designs for a project in the 1990s. I used a random pattern and sizing akin to a golf ball. It did not work for supersonic in the model, but I did not spend much time on it and my graduate advisor thought it was stupid.

Later, working on a different project, we were able to extend the range of dimpled steel balls that were propelled at about 3,000 fps, but there was no rifling.

I am sure there are some things that are possible, but not practical given current components. When poly cases become a thing, some of those might come to light.
 
Had no idea that was a thing. Thank you for that. Though it's more of an attempt to extend the supersonic speed out by a large factor, so similar end goal.
 
Or any more airfoil-shaped bullets to perhaps not do so well in supersonic, but yet maintain momentum through the transsonic regime?
Click to expand...

A boat-tail bullet takes advantage of the characteristics of the expansion wave just like a supercritical airfoil.
 
See 3:50 and on in this video . You can see what it looks like when a bullet is right in or just below the transonic zone and how the bullet is struggling to stay straight . It also explains what Markco was saying and how even though the tip of the bullet is subsonic the air passing over it is supersonic when you're just under supersonic speeds . IMHO It's those shock waves on the bullet in the transonic zone that destabilizes the bullet and disrupts the bullets flight path . I'd assume bullet shape , weight and spin rate all have an effect on how the bullet handles the transonic zone .
https://www.youtube.com/watch?v=BPwdlEgLn5Q
 
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